Metal Toxicity, Oxidative Stress and Antioxidative Defense System in Plants

Department of Biochemistry, Faculty of Science, Banaras Hindu University, Varanasi-221005, India, Fax: 91-542-2368174, E-mail: rsdbhu@rediffmail.com Introduction Contamination of soil with metals has become a major global environmental problem, specially in areas with high anthropogenic pressures, leading to losses in agricultural yield and threat to the health of wildlife and humans (Salt et al. 1998, Sharma and Dubey 2007, Sharma and Dietz 2008). Metal pollutants which are non-essential for plants and are commonly used in industrial processes, which contaminate soil environment include Pb, Cd, Hg, Cr, As (Scott and Smith 1981), whereas certain essential metals that serve as micronutrients for plants but accumulate in high concentrations in the soil due to diverse anthropogenic activities include Fe, Cu, Ni, Zn (Mishra and Dubey 2006). Excessive concentrations of the metals in the soil environment may arise due to various processes such as mining, presence of naturally occurring ore bodies, metalwork industries, urban traffi c, power stations, exploitation of natural resources, agricultural practices including wastewater irrigation, waste disposal, etc. (Pinto et al. 2003, Sharma et al. 2007). High levels of metals in the soil infl uence soil properties and adversely affect establishment and growth of plants whose roots initially develop in the contaminated layer. Uptake of metals by plants is a complex phenomenon which depends on the ionic potential of the metal, its ionic radii, etc. and may involve several steps including participation of specifi c metal transporters across the plasma membrane of root cells, xylem loading and translocation (Bernal et al. 2007, Sharma and Dietz 2008).